(Supported in part by NSF MCB 9408249 to J. Aist). This project is currently in progress. Its goals are to determine where the forces are generated to separate the spindle poles during anaphase B in the fungus Nectria haematococca, and to investigate the role of cytoplasmic dynein in mitosis, nuclear migration and nuclear positioning. To achieve the first two goals the laser microbeam is used to sever spindles during anaphase in control cells and in cytoplasmic-dynein mutants. To achieve the latter two goals the optical trap is used to measure the relative forces needed to arrest nuclear migration, and displace nuclei, in controls and mutants. To date the data reveal that the spindle poles pull themselves apart during anaphase and that this process is mediated by cytoplasmic dynein. Parts of this work have been abstracted to the 1997 ASCB meeting and two papers are currently being prepared for publication. Inoue, S., O.C. Yoder, B.G. Turgeon and J.R. Aist. (1997) Cytoplasmic dynein is essential for formation and function of asters in the fungus Nectria haematococca. Molec. Biol. Cell 8: